<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>牛</button>
    <script>
        let num = 10;
        console.log(num);
        if (true) {
            let b = 20;
            console.log(b);
            if (true) {
                let c = 30;
            }


        }
        // console.log(b);
        for (var i = 0; i < 9; i++) {

        }
        console.log(i);
        for (let j = 0; j < 9; j++) {
            console.log(j);

        }
        // console.log(j);
        // 暂时性死区
        var tmp = 123;
        if (true) {
                tmp = 'avd';
                // let tmp;
            }
            console.log(tmp);
    </script>
</body>

</html>